John Carney’s low budget 2006 musical romance “Once” was a breakout hit that foregrounded the emotional complexities of its central lovers with delicate tunes. By contrast, “Can a Song Save Your Life?” — which contains several high profile actors and landed a lucrative deal with The Weinstein Company this past week at the Toronto International Film Festival — revolves around the exploitation of that very same feeling. The story centers on forlorn aspiring British songwriter Gretta (Keira Knightley) adrift in Manhattan after getting dumped by her philandering rock star boyfriend (Adam Levine) and being discovered by struggling music producer Dan (Mark Ruffalo). Eager for a fresh discovery, Dan pushes Gretta to sign with him and record an ambitious outdoors album all across the city. She’s initially reticent; songwriting is just something that she does. “Can a Song Save Your Life?” explores this tension with a blithe attitude that foregrounds several enjoyable melodies performed throughout the movie, but it also feels every bit as commercial as the world it disparages.

Executive produced by Judd Apatow, Carney’s movie revolves around a familiar set of character types that wouldn’t seem out of place in a studio comedy like the ones Apatow tends to make. Yet it works significantly better than more mainstream productions because of the legitimacy its actors bring to the project. Knightley’s sorrowful state plays nicely off Ruffalo’s sputtering showbiz enthusiasm. His character’s own background would strain from contrived ingredients if it weren’t so credibly embodied: His relationship to his wife (Catherine Keener) remains on the rocks following an earlier affair, while his angst-riddled daughter (Hailee Steinfeld) copes with her burgeoning womanhood under her parents’ close watch. Meanwhile, Dan’s longtime producing partner (Mos Def) wants to kick him out of the venture since he’s unwilling to embrace mainstream trends in the industry. The movie’s title doesn’t lie: Gretta’s talent has the potential to give Dan’s career meaning again just as it can rescue her for her sorrows.

“Can a Song Save Your Life?” explores this scenario with a light touch but plenty of entertainment value. The stakes are nicely established with Knightley’s performance of a solemn tune about loneliness during an acoustic set forced on her by friend: Hesitant to share her work with the world, she has zero stage presence. But minutes later we witness the scene a second time from Ruffalo’s perspective. Drunk and frustrated with his flagging career, the character perks up when he hears the music and gazes at the performer with a giddy smile as the movie assumes his perspective. Behind Knightley, the other instruments suddenly become animated by an invisible hand as Dan imagines the potential for Gretta’s music in the hands of a good producer and backup musicians. It’s the only moment of genuine magical realism that makes the movie’s soundtrack come alive in a truly dynamic way. Dan’s drive to sign Gretta based on this experience gives the premise a fairy tale quality that makes it easy to invest in his mission: We’ve seen the same potential that he has.

The bulk of “Can a Song Save Your Life?” doesn’t try as hard to complicate the drama. Despite its musical interludes, the plot unfolds as a fairly straightforward crowd pleaser that barely reaches for heavy sentiments. Following a cheeky cameo by Cee Lo as the posh musician willing to finance Gretta’s album, there’s no doubt whether Dan can find the resources he needs to get back on track. Gretta’s mopey relationship with her ex fills more screen time than necessary considering that he’s a largely flat character that she’ll eventually get over. After a while, the only real star of “Can a Song Save Your Life?” is its original compositions.

Yet few of them stand out. Most of Gretta’s performances, while sweet to the ear, lack much ingenuity. Performing on rooftops and alleyways while Dan grins from the sidelines — and at one point joins in — Gretta delivers a series of tracks with a genial presence that makes the case for her star potential, but slows the movie down for sequences that have the stationary quality of a concert documentary.

Fortunately, the narrative of “Can a Song Save Your Life?” is significantly better than that. Moving along at a reasonably engaging pace, it foregrounds the actor’s investment in the scenario and makes it relatable. The occasional moments when the story veers into whimsical territory — as when Gretta records a song on her ex-boyfriend’s voicemail to announce her frustrations with him, or when she traipses around the city with Dan listening to jazz on his headphones — Carney delivers an infectious sense for music’s cathartic power. But as a whole, it’s a fairly mannered treatment of an expressive medium. “We need vision, not gimmicks,” Dan’s partner tells him. “Can a Song Save Your Life?” struggles against that advice throughout.

Criticwire grade: B

HOW WILL IT PLAY? Acquired by The Weinstein Company after its Toronto premiere, the movie stands to perform decently if its vibrant soundtrack takes off and word of mouth remains strong.